1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal display panel capable of preventing air from flowing into an image display part of a liquid crystal display panel where a thin film transistor array substrate and a color filter substrate are attached to each other.
2. Discussion of the Related Art
In general, a liquid crystal display device is a display device where data signals including picture information are individually supplied to liquid crystal cells arranged in a matrix form. The light transmittance of the liquid crystal cells is controlled based on these data signals to display a desired picture.
Thus, the liquid crystal display device includes a liquid crystal display panel where the pixels are arranged in a matrix, and where a driver integrated circuit (IC) drives the pixels.
In the liquid crystal display panel, a thin film transistor array substrate and a color filter substrate face each other, but they are separated from each other by a certain predetermined distance generally referred to as a cell-gap. A liquid crystal layer is formed in this cell gap.
The thin film transistor array substrate and the color filter substrate are attached to each other by a seal pattern formed along the outer edge of an effective image display portion of the LCD panel. When the seal pattern is formed, a spacer is formed on the thin film transistor array substrate or on the color filter substrate, to provide the desired cell-gap therebetween.
On outer surfaces of these substrates, other components such as a polarizing plate, a retardation plate and the like are installed. These other components are selected so as to vary the propagation of light and the refraction ratio in order to construct a liquid crystal display device having a high brightness and contrast characteristics.
On the portion of the liquid crystal display panel where the thin film transistor array substrate and the color filter substrate face each other, a common electrode and a pixel electrode are formed. These electrodes are used to apply an electric field to the liquid crystal layer. That is, a voltage applied to the pixel electrode is controlled by the voltage applied to the common electrode. In doing so the light transmittance of the pixels can be individually controlled. In order to independently control the voltage applied to the pixel electrode of each pixel by unit pixel, a thin film transistor formed at each pixel is used as a switching device.
Liquid crystal display devices are generally classified into two categories: twisted nematic (TN) mode liquid crystal displays and in-plane switching (IPS) mode liquid crystal display panel.
In the TN mode liquid crystal display, a pixel electrode for each individual pixel is formed on a thin film transistor array substrate. In addition, a common electrode is formed on an entire surface of a color filter substrate. Thus, the liquid crystal layer is driven by an electric field between the pixel electrodes formed on the thin film transistor array substrate and the common electrode formed on the color filter substrate.
In the IPS mode liquid crystal display, both a pixel electrode and a common electrode are formed on a thin film transistor array substrate a certain distance apart. The liquid crystal layer is driven by the horizontal electric field between the pixel electrode and the common electrode formed on the thin film transistor array substrate.
FIG. 1 is a plane view illustrating the typical structure illustrates a plane structure of a TN mode liquid crystal display panel in which the thin film transistor array substrate and the color filter substrate face each other and are attached to each other by a seal pattern.
In FIG. 1, the thin film transistor array substrate 101 faces and is attached to the color filter substrate, with an edge of one long side thereof and an edge of one short side thereof ate protruded beyond the respective edges of the color filter substrate 102.
In a region where the substrates 101 and 102 face each other, an image display part 113 is provided, where pixels are formed in a matrix. A seal pattern 116 is formed along the outer edge of this image display part 113.
A gate pad part 114 connected to gate lines of the image display part 113 is provided at an edge region of the short side of the thin film transistor array substrate 101 that protrudes beyond the color filter substrate 102.
A data pad part 115 connected to data lines of the image display part 113 is provided at an edge region of the long side of the thin film transistor array substrate 101 that protrudes beyond the color filter substrate 102.
The gate pad part 114 supplies a scan signal from a gate driver integrated circuit to the gate lines of the image display part 113. The data pad part 115 supplies image information from a data driver integrated circuit to the data lines of the image display part 113.
The gate lines to which the scan signal is applied and the data lines to which the image information is applied intersect one another on the thin film transistor array substrate 101 to define a matrix of pixels. A thin film transistor is provided at each intersection for switching the pixel at that intersection.
A red, green or blue color filter corresponding to a pixel is provided on the color filter substrate 102. A black matrix is also provided to prevent the leakage of light generated by a back-light and to prevent the mixing of colors from adjacent unit pixels.
In the TN mode liquid crystal display panel, a pixel electrode is provided at the thin film transistor array substrate 101, and a common electrode is provided at the color filter substrate 102 to drive a liquid crystal layer. In the IPS mode liquid crystal display panel, both pixel electrode and a common electrode are provided at the thin film transistor array substrate 101 to drive a liquid crystal layer.
The thin film transistor array substrate 101 and the color filter substrate 102 a cell-gap separating them. The cell-gap is maintained by a spacer so that the substrates remain separated from each other. The substrates are attached to each other by a seal pattern 116 formed along the outer edge of the image display part 113. A liquid crystal injection hole is provided on one side of the seal pattern 116 for injecting liquid crystal between the thin film transistor array substrate 101 and the color filter substrate 102. The liquid crystal injection hole is sealed after the injection of the liquid crystal is complete.
The cell-gap between the thin film transistor array substrate 101 and the color filter substrate 102 is constant at the image display part 113, but it varies in the region where the seal pattern 116 is formed because the sealant is pressed and spread by the pressure applied during assembly to attach the thin film transistor array substrate 101 to the color filter substrate 102.
In order to prevent the size of the cell-gap from varying, a glass fiber or a glass ball is added to the seal pattern 116 as a support member for maintaining the cell-gap.
FIG. 2 is a sectional view illustrating a color filter substrate for a region ‘A’ of FIG. 1 in an IPS mode liquid crystal display panel.
With reference to FIG. 2, a color filter substrate of an IPS mode liquid crystal display panel includes a black matrix 202 made of a resin material patterned at a region separated by a fixed distance from one end portion of a transparent substrate 201 and a boundary region of pixels. The black matrix prevents leakage of light generated from a back-light and prevents a mixture of colors from adjacent pixels. A red, green, or blue color 203 partially overlaps the black matrix corresponding to a unit pixel. An over-coat layer 204 is formed on an entire surface of an upper portion of the transparent substrate 201, including the black matrix 202 and the color filter 203. A seal pattern 206 is formed on an upper surface of the over-coat layer 204 formed on the edge of the transparent substrate 201 so as to partially overlap the black matrix 202.
The black matrix 202 formed at the color filter substrate of the IPS mode liquid crystal display panel is made of a resin material.
The over-coat layer 204 is formed on an entire surface of the upper portions of the black matrix 202 and the color filter 203 to planarize a surface. That is, because a black matrix 202 formed of an organic film such as a resin material is applied as a thick film, the over-coat layer 204 is also formed of an organic material in order to prevent a deficiency in driving a liquid crystal layer which is caused by a step occurring at the region where the black matrix 202 and the color filter 203 overlap with each other.
As stated above, a glass fiber or a glass ball is added to the seal pattern 206 as a support member for maintaining a cell-gap.
FIG. 3 illustrates a magnified view of the distribution of glass fibers added to the inside of the seal pattern 206.
A seal pattern 206 is formed at an upper surface of a black matrix 202 or at an over-coat layer 204 formed of an organic film material. As the glass fiber 207 added to the seal pattern 206 it depresses the black matrix 202 and the over-coat layer 204 from external pressure caused during or after attaching the thin film transistor array substrate to the color filter substrate cracks form at the interfaces between the over-coat layer 204 and the black matrix 202, and between the black matrix 202 and the transparent substrate 201. Outside air flows into the image display part through the cracks, thereby degrading the quality of the liquid crystal display panel. This will be described in detail with reference to FIGS. 4a and 4b. 
FIGS. 4a and 4b illustrate an organic film black matrix 302 formed of a resin material patterned at a region separated by a fixed distance from one end portion of a first transparent substrate 301 and at a boundary region of pixels so as to prevent leakage of light generated from a back-light and so as to prevent a mixture of colors from adjacent pixels. A red, green or blue color filter 303 is formed so as to partially overlap with the black matrix 302 such that it corresponds to a pixel. An over-coat layer 304 formed of an organic film, and is formed at an entire surface of an upper portion of the first transparent substrate 301 including the black matrix 302 and the color filter 303. A seal pattern 306 is formed on an upper surface of the over-coat layer 304 that is formed along an edge portion of the first transparent substrate 301 so as to partially overlap with the black matrix 302. A glass ball or glass fiber 307 is added to the seal pattern 306, thereby maintaining a cell-gap distance in the region where the seal pattern 306 is formed. The glass ball or glass fiber 307 has a diameter which is the same as or greater than the cell-gap.
First, as shown in FIG. 4a, in a normal state the glass ball or the glass fiber 307 added to the seal pattern 306 can maintain a cell-gap distance by coming in contact with a thin film transistor array substrate (not shown) and the over-coat layer 304 therebetween.
However, as shown in FIG. 4b, as the glass ball or the glass fiber 307 is pressed by external pressure during or after assembly of the liquid crystal display panel, the black matrix 302 and the over-coat layer 304 are compressed. As the black matrix 302 and the over-coat layer 304 formed of an organic material are compressed, cracks form at interfaces between the over-coat layer 304 and the black matrix 302, and between the black matrix 302 and a first transparent substrate 301. Outside air flows into the image display part through the cracks, thereby degrading and contaminating the liquid crystal display panel, and the seal pattern 306.
As described above, in the related art IPS mode liquid crystal display panels, a glass fibers or a glass balls maintaining a cell-gap distance between the thin film transistor array substrate and the color filter substrate are added to the seal pattern that attaches the thin film transistor array substrate to the color filter substrate. But, when external pressure is used during or after attaching the thin film transistor array substrate to the color filter substrate, outside air flows into the image display part, degrading the quality and performance of the liquid crystal display panel and breaking the seal pattern.